Extracorporeal circulation of blood has been performed in surgical procedures such as open heart surgery for many years. An important component in the extracorporeal blood circuit is a blood oxygenator. The function of the oxygenator is to place oxygen in close relationship to the venous blood so that the oxygen reacts with the hemoglobin with resultant absorption of the oxygen and release of carbon dioxide.
Various types of blood oxygenators are in use. Among the most popular is the type known as the "bubble oxygenator" wherein bubbles of oxygen are introduced directly into the blood. One consequence of using a bubble oxygenator is that once the blood has been arterialized by the introduction of oxygen bubbles, these bubbles must be removed from the blood before the blood is returned to the patient's body, since the presence of gaseous bubbles in the patient's bloodstream can be injurious and substantial amounts of bubbles may lead to death. Therefore, bubble oxygenators typically incorporate some sort of defoaming means which collapses the bubbles in the blood, thereby separating the residual oxygenating gas from the liquid arterialized blood before the blood is reintroduced to the patient.
One type of bubble oxygenator with defoaming means, which has been employed with highly successful results for several years, is disclosed in U.S. Pat. Nos. 4,065,264; 4,138,288 and 4,138,464. In this type of device, the defoaming element is an annular body of porous, reticulated, open-cell polyurethane foam positioned within a cylindrical housing upon a generally disc-shaped base. The defoaming element is surrounded by a layer of woven nylon or polyester fabric, which serves as a final barrier against the passage of gaseous bubbles, as well as any solid particulate matter that may be present in the arterialized blood, to the patient. The polyurethane defoaming element is treated with an anti-foam compound such as a polydimethylsiloxane compound. The arterialized blood flows radially, from the inside to the outside, through the annular element and surrounding layer of fabric and into a substantially annular defoamed blood reservoir, which includes the space between the layer of fabric and the housing and an extension of this space below the level of the generally disc-shaped base. In this known type of device, the layer of fabric surrounding the polyurethane defoaming element has heretofore been tied to the base (upon which the defoaming element is positioned) by means of a pair of nylon tie straps. Use of this tying means, however, introduces a potential problem. As defoamed blood first accumulates in the substantially annular reservoir, the possibility exists that air bubbles may be formed and trapped against the undersides of the heads of the tying straps or the straps themselves. The presence of gas bubbles downstream of the above-mentioned layer of fabric would clearly be undesirable. Additionally, it would be beneficial to improve the known type of device by providing a seal between the base and said layer of fabric that essentially eliminated any possibility of blood flow bypass around the layer of fabric and was easy to form during the manufacture of the defoaming device.